1. Field of the Invention
The present invention relates to a steering wheel for a vehicle having an airbag apparatus. More particularly, the invention relates to a steering wheel having an airbag apparatus and in which switch operating portion of a function part is disposed. Examples of the function part are drive monitor switch, constant-speed running apparatus, audio equipment, air conditioner equipment, navigation system, telephone, shift change and the like.
2. Description of Related Art
Conventionally, a steering wheel having an airbag apparatus is know in Japanese Patent Applications Laid-open No.100907/1998 and No.11246/1999. The airbag apparatus comprises an airbag, an inflator, a pad and a bag holder. The airbag is folded such that the airbag can expand. The inflator supplies expansion gas to the airbag. The pad covers the folded airbag. The bag holder holds the airbag, the inflator and the pad, and is connected to a steering wheel body.
The pad includes a door that is pushed by the expanding airbag and opened. The door is provided at its periphery with a to-be ruptured portion, and is provided at its portion of an outer periphery with a hinge. The door is pushed when the airbag expands to rupture the to be ruptured portion, and opens around the hinge as a rotation center.
In these days, it is increasingly required to dispose switch operating portions for the function part that are drive monitor switch, constant-speed running apparatus, audio equipment, air conditioner equipment, navigation system, telephone, shift change and the like on the pad of the boss or the spokes near the boss. These switch operating portions are constituted such that they can be operated from above. That is, the switch operating portion comprised operation button or operation lever operated by being pushed downward or swung. In order to facilitate the operation of the switch operating portion, the switch operating portion is disposed upward such that its operating surface approaches a ring surface. The ring surface is the plane formed by an upper surface of a ring when the steering wheel is viewed from a direction perpendicular to a steering shaft.
However, when the airbag is developed and expanded when a driver is close to the steering wheel, it is necessary that the airbag does not apply a partial pushing force to the driver. For this purpose, it is preferable to develop the airbag widely at initial stage of expansion and to inflate the airbag toward the driver. At that time, if the door of the pad interferes with the switch operating portion uselessly, the door can not open widely. That is, the airbag at its initial expanding stage can not be developed widely.
In the present specification, the upper-lower, front-rear and right-left directions are based on the steering shaft when the steering wheel is mounted to the vehicle unless otherwise stated. That is, the upper-lower direction in the present specification is a vertical direction along the axial direction of the steering shaft. The front-rear direction in the present specification is the front and rear direction (a longitudinal direction) of the vehicle along a direction perpendicular to the axis of the steering shaft when the steering wheel is steered straightly.